1. Field of the invention
The present invention concerns a method for the thermochemical treatment of metals by deposition of materials onto a substrate to be treated.
It is more particularly concerned with a physical vapor deposition (PVD) method in which the substance of a target which constitutes a first electrode of an ion bombardment treatment furnace is evaporated and the particles produced in this way are deposited onto a substrate constituting a second electrode at a potential different than that of the first electrode.
Of course, during this process the substrate is heated to the treatment temperature by the heat generated by the ion bombardment or by heating means provided inside the furnace, or even by a combination of these two means.
2. Description of the prior art
Until now the treatment temperature has been held below a particular threshold in the order of 500.degree. C. to avoid exceeding the tempering temperature of the quenched steel and so to prevent deterioration of the mechanical properties of the parts treated (hardness, tensile strength, etc) such as are observed in practice when this temperature is exceeded. Also, it has been necessary to eliminate the risk of deformation of the treated parts and to remain within the temperature range allowed for the target and for the means used to monitor its evaporation.
This temperature limit was essential when using a magnetron to generate a magnetic field at the surface of the target to enhance evaporation without melting the target.
It is clear that in this case the treatment temperature produced inside the furnace must be as far away as possible from the melting point of the target and that this temperature is not high enough to damage the electromagnet circuit of the magnetron.
Furthermore, increasing the temperature above said threshold went counter to an advantage resulting from the use of a magnetron whereby heating of the substrate as a result of its bombardment with high-energy electrons from the target is reduced.
A particular object of the invention is to improve the quality of the thermochemical treatment previously described, in particular with reference to the regularity of the deposit (thickness, roughness), its adherence to the substrate and the treatment time. Another object is to master the treatment of depositing metal halogenides which were previously difficult to use or entailed the use of highly toxic elements. It is further directed to expanding the range of deposition treatments, in particular by enabling deposition of interdiffused multilayers or binary or ternary alloys and deposition followed by quenching.